Equation of State of Protoneutron Star with Trapped Neutrinos

The influence of trapped neutrinos on the proto-neutron star is studied in the framework of relativistic mean-field theory. The results show that trapped neutrinos increase proton fraction and make the equation of ๏๏ state of neutron star matter softer when neglecting hyperonic freedom, while suppress the appearance of hyperons and make the equation of state stiffer when including hyperons in the protoneutron star. The maximum mass, compared with cold neutron star which is in beta equilibrium, decreases by 0.06_{M_{\odot}} for non-strange protoneutron star while increases by 0.21_{M_{\odot}} for protoneutron star with hyperons when the relative number of trapped neutrino is 0.4.     

Phase Transitions in Neutron Stars Within Modified Quark-Meson Coupling Model

K^- condensation and quark deconfinement phase transitions in neutron stars are investigated. We use the modified quark-meson coupling model for hadronic phase and the MIT bag model for quark phase. With the equation of state (EOS) solved self-consistently, we discuss the properties of neutron stars. We find that the EOS of pure hadron matter with condensed K^- phase should be ruled out by the redshift for star EXO0748-676, while EOS containing unpaired quark matter phase with B^1/4 being about 180 MeV could be consistent with both this observation and the best measured mass of star PSR 1913+16. But if the recent inferred massive star among Terzan 5 with M>1.68M_๏ is confirmed, all the present EOSes with condensed phase and deconfined phase would be ruled out.     

Hadron masses in medium and neutron star properties

We investigate the properties of the neutron star with relativistic mean-field models. We incorporate in the quantum hadrodynamics and in the quark-meson coupling models a possible reduction of meson masses in nuclear matter. The equation of state for neutron star matter is obtained and is employed in Oppenheimer-Volkov equation to extract the maximum mass of the stable neutron star. We find that the equation of state, the composition and the properties of the neutron stars are sensitive to the values of the meson masses in medium.     

Nucleon Finite Volume Effect and Nuclear Matter Properties in a Relativistic Mean-Field Theory

Effects of excluded volume of nucleons on nuclear matter are studied, and the nuclear properties that follow from different relativistic mean-field model parametrizations are compared. We show that, for all tested parametrizations, the resulting volume energy al and the symmetry energy J are around the acceptable values of 16 MeV and 30 MeV, and the density symmetry L is around 100 MeV. On the other hand, models that consider only linear terms lead to incompressibility Ko much higher than expected. For most parameter sets there exists a critical point （pc, δc）, where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero. This critical point depends on the excluded volume parameter r. If this parameter is larger than 0.5 fm, there is no critical point and the pure neutron matter is predicted to be bound. The maximum value for neutron star mass is 1.85M⊙, which is in agreement with the mass of the heaviest observed neutron star 4U0900-40 and corresponds to r = 0.72 fm. We also show that the light neutron star mass （1.2M⊙） is obtained for r ≌ 0.9 fro.     

Influence of the nuclear equation of state on the hadron-quark phase transition in neutron stars

We study the hadron-quark phase transition in the interior of neutron stars, and examine the influence of the nuclear equation of state on the phase transition and neutron star properties. The relativistic mean field theory with several parameter sets is used to construct the nuclear equation of state, while the     

Effect of Mesons f0(975) and $\phi(1020)$ and Variety of $U_\Xi^{(N)}$ on Properties of Neutron Star Matter

We examine the effect of adding mesons f₀(975) and $\phi(1020)$ as well as the variety of $U_\Xi^{(N)}$ (the potential well depth of $\Xi$ in nuclear matter) from -10 MeV to -28 MeV on the extent of the particles participation and the properties of the neutron star in the relativistic mean field model. We find that considering the contribution of f₀ and $\phi$ mesons, the equation of state of the neutron star turns soft, the maximum mass reduces while the corresponding radius increases. $\Xi^-$ hyperons appear at lower density as $U_\Xi^{(N)}$ becomes deeper, and the variety of $U_\Xi^{(N)}$ has little effect on the equation of state and the properties of the neutron star.     

利用非对称核物质状态方程对中子星的质量和半径的研究

在温度、密度及同位旋相关的核物质状态方程的基础上,通过求解Tol-man-Oppenheimer?Volkoff方程得到了中子星的质量与中心密度的关系,发现随着中心密度的变化,中子星存在一个最大质量.同时计算结果表明,中子星的最大质量与核物质状态方程的不可压缩系数、有效质量及对称能强度系数等密切相关.对中子星半径的研究表明,较硬的核物质状态方程给出的中子星半径较大,而且较大的对称能强度系数和较大的核子有效质量也会给出较大的中子星半径.     

Neutron stars including the effects of chaotic magnetic fields and anomalous magnetic moments

The relativistic mean field(RMF) FSUGold model extended to include hyperons is employed to study the properties of neutron stars with strong magnetic fields.The chaotic magnetic field approximation is utilized.The effect of anomalous magnetic moments(AMMs) is also investigated.It is shown that the equation of state(EOS)of neutron star matter is stiffened by the presence of the magnetic field,which increases the maximum mass of a neutron star by around 6%.The AMMs only have a small influence on the EOS of neutron star matter,and increase the maximum mass of a neutron star by 0.02M_(sun).Neutral particles are spin polarized due to the presence of the AMMs.     

Study of the asymmetric nuclear matter with pion dressing

We discuss here a self-consistent method to calculate the properties of the cold asymmetric nuclear matter. The nuclear matter is dressed with s-wave pion pairs. The nucleon-nucleon (N-N) interaction is mediated by these pion pairs, ∞ and ρ mesons. The parameters of these interactions are calculated selfconsistently to obtain the saturation properties like equilibrium binding energy, pressure, compressibility and symmetry energy. The computed equation of state is then used in the Tolman-Oppenheimer-Volkoff (TOV) equation to study the mass and radius of a neutron star containing pure neutron matter.     

Bose-Einstein condensation of anti-kaons and neutron star twins

We investigate the role of Bose-Einstein condensation (BEC) of anti-kaons on the equation of state (EoS) and other properties of compact stars. In the framework of relativistic mean field model we determine the EoS for β-stable hyperon matter and compare it to the situation when anti-kaons condense in the system. We observe that anti-kaon condensates soften the EoS, thereby lowering the maximum mass of the stars. We also demonstrate that the presence of antikaon condensates in the high density core of compact stars may lead to a new mass sequence beyond white dwarf and neutron stars. The limiting mass of the new sequence stars is nearly equal to that of neutron star branch though they have distinctly different radii and compositions. They are called neutron star twins.     

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K⁰ condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m_s and the color superconducting gap Δ. Increasing B and m_s or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars.     

LOCV calculation of the equations of state and properties of rapidly rotating neutron stars

In this paper, we have investigated the structural properties of rotating neutron stars using the numerical RNS code and equations of state which have been calculated within the lowest order constrained variational(LOCV)approach. In order to calculate the equation of state of nuclear matter, we have used UV_(14) +TNI and AV_(18) potentials.We have computed the maximum mass of the neutron star and the corresponding equatorial radius at different angular velocities. We have also computed the structural properties of Keplerian rotating neutron stars for the maximum mass configuration, M_K, R_K, f_K and j_(max).     

Equation of state in hybrid stars and the stability window of quark matter

Properties of hybrid stars with a mixed phase composed of asymmetric nuclear matter and strange quark matter are studied. The quark phase is investigated by the quark quasiparticle model with a self-consistent thermodynamic and statistical treatment. We present the stability windows of the strange quark matter with respect to the interaction coupling constant versus the bag constant. We find that the appearance of the quark–hadron mixed phases is associated with the meta-stable or unstable regions of the pure quark matter parameters. The mass–radius relation of the hybrid star is dominated by the equation of state of quark matter rather than nuclear matter. The contour plots of the maximum mass of the hybrid star are shown in the plane of the coupling constant and the bag constant.     

Hypernuclear physics for neutron stars

The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon–nucleon and hyperon–hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Nonmesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.     

Plan for nuclear symmetry energy experiments using the LAMPS system at the RIB facility RAON in Korea

We review the calculation of the equation of state of pure neutron matter using quantum Monte Carlo (QMC) methods. QMC algorithms permit the study of many-body nuclear systems using realistic two- and three-body forces in a non-perturbative framework. We present the results for the equation of state of neutron matter, and focus on the role of three-neutron forces at supranuclear density. We discuss the correlation between the symmetry energy, the neutron star radius and the symmetry energy. We also combine QMC and theoretical models of the three-nucleon interactions, and recent neutron star observations to constrain the value of the symmetry energy and its density dependence.     

Hybrid stars and quark hadron phase transition in chiral colour dielectric model

We investigate the properties of hybrid stars consisting of quark matter in the core and hadron matter in outer region. The hadronic equation of state (EOS) is calculated by using nonlinear Walecka model. Strange baryons are included in the hadronic EOS calculation. The chiral colour dielectric (CCD) model, in which quarks are confined dynamically, is used to calculate quark matter EOS. We find that the phase transition from hadron to quark matter is possible in a narrow range of the parameters of nonlinear Walecka and CCD models. The transition is strong or weak first order depending on the parameters used. The EOS thus obtained, is used to study the properties of hybrid stars. We find that the calculated hybrid star properties are similar to those of pure neutron stars.     

新生中子星的性质与三体核力效应

在Brueckner-Hartree-Fock理论框架内, 研究了新生中子星的状态方程和性质, 计算了新生中子星的最大质量和新生中子星中质子占总核子数的丰度, 特别是讨论了三体核力和中微子束缚效应的影响以及三体核力和中微子束缚效应的相互影响. 结果表明, 无论是否考虑三体核力, 中微子束缚对新生中子星的状态方程和质子丰度均有明显影响. 中微子束缚导致新生中子星物质中的质子丰度显著增大. 三体核力的贡献是使新生中子星的状态方程变硬并导致新生中子星中质子丰度明显增大. 束缚在中子星物质中的中微子显著减弱了三体核力对于中子星物质中质子丰度的影响.     

Vacuum renormalization of the chiral-sigma model and the structure of neutron stars

Vacuum renormalization corrections are calculated for normal nuclear matter and neutron star matter in the chiral-sigma model. The theory is generalized to include hyperons in equilibrium with nucleons and leptons. The equations of state corresponding to two compression moduli, a “stiff” and “soft” one for nuclear matter, are studied. It is shown that fully one half the mass of a neutron star at the limiting mass is composed of matter at less than twice nuclear density. Neutron star masses are therefore moderately sensitive to the properties of matter near saturation and to the domain of the hyperons, but dominated by neither. The predictions for the two equations of state are compared with observed neutron star masses, and only the stiffer is compatible.     

Hadrons in compact stars

We discuss β-equilibrated and charge neutral matter involving hyperons and {ie817-1} condensates within relativistic models. It is observed that populations of baryons are strongly affected by the presence of antikaon condensates. Also, the equation of state including {ie817-2} condensates becomes softer resulting in a smaller maximum mass neutron star